1. Field of the Invention
The present invention generally relates to a method and apparatus for reconstructing the position of a high dose rate (HDR) source in three-dimensional (3D) space in real-time using a flat panel detector (FPD) and can be used to compare the detected position with the path produced by the treatment plan.
2. Background Description
Brachytherapy involves two distinct phases, a planning phase and a treatment phase. The planning phase, which produces a treatment plan, typically involves subjecting the patient to CT scan, an MRI or ultrasound imaging in order to determine the 3D coordinates of the locations within the patient's body where radiation therapy is to be applied. The treatment phase requires placing the radiation emitting or HDR source at those locations determined in the planning phase according to the treatment plan.
During HDR treatments, the source follows a path through catheters and applicators based on a plan produced by the treatment planning phase. A number of Quality Assurance (QA) procedures are put in place to safely deliver a treatment as planned. Evaluating whether the treatment is or has been delivered as planned is difficult because a typical treatment plan is a list of source positions and time intervals. The source position may be defined as distances from/the end of the catheter along the catheter (i.e., along a trajectory). In order to compare the applied treatment with the planned treatment, the planned source positions and the reconstructed source positions have to be expressed in the same coordinate system. Thus, a correspondence between a detection coordinate system and a planned coordinate system has to be established. As known in the art, such a conversion is generally an overlap of a 3D translation and a 3D rotation with a scale factor, if necessary. The problem of establishing a correspondence between a detection coordinate system and a plan coordinate system is even more complex due to the manner in which the plan sets forth the source positions (i.e., distances on a trajectory from an end thereof). Conventionally, it was assumed that the plan was delivered as intended, but no feedback was generated. That is, no comparison of applied treatment with the planned treatment was performed. Moreover, this must be done in real time, to determine that the real HDR positions and the dwell times correspond to the treatment plan. This might be done using, for example, a fluroscope image of the catheter. However, this procedure subjects the patient to a double dose of radiation if the planning phase was conducted using a CT scan, for example. The Nuclear Regulatory Commission (NRC) prohibits using two sources of radiation simultaneously (for instance an X-ray source for imaging and an HDR source for treatment delivery).